It looks like a jewelry shop with its high-end exterior. But a peek inside the sparkling glass display cases at any of Sembikiya's Tokyo outlets reveals expensive treasures of a surprising kind.

The Japanese are renowned for being perfectionists and when it comes to food, Japan leads the way. From heart-shaped watermelons to "Ruby Roman" grapes, which are the size of a ping pong ball, this retailer specializes in selling mouth-watering produce at eye-watering prices.

Across Japan, such products regularly sell for tens of thousands of dollars at auction. In 2016, a pair of premium Hokkaido cantaloupe sold for a record $27,240 (3 million yen). "Fruits are treated differently in Asian culture and in Japanese society especially," Soyeon Shim, dean of the School of Human Ecology at the University of Wisconsin-Madison, tells CNN. "Fruit purchase and consumption are tied to social and cultural practices.

"It is not only an important part of their diet, but, perhaps more importantly, fruit is considered a luxury item and plays an important and elaborate ritual part in Japan's extensive gift-giving practices."

Cultivating high-end produce usually involves meticulous, labor-intensive practices developed by Japanese farmers.

"It's hard getting the shape of these strawberries right -- they can sometimes turn out like globes," says Okuda Nichio, of his highly-prized Bijin-hime (beautiful princess) strawberries, which he tries to grow "scoop-shaped".

"It's taken me 15 years to reach this level of perfection."

Nichio's strawberries each take 45 days to grow at his Okuda farm in Gifu prefecture, and although he won't go into detail about how they are produced -- "I can't tell you exactly what the methods are because otherwise everyone else will catch on" -- he believes it is time well spent.

His largest tennis-ball sized strawberries, of which he only produces around 500 a year, usually sell for more than 500,000 yen ($4,395) each. Rarity is a tactic also employed by the producers of Japan's "Ruby Roman" grapes, who offer just 2,400 bunches of the large red fruit each year.

The grapes were cultivated to fill a gap in the Japanese luxury fruit market, according to Ruby Roman spokesman Hirano Keisuke. Holding just 30 grapes in total, that record-breaking bunch essentially sold for $320 per grape.